Rolf

When Styrofoam is used in boats they call it EPS. It is very strong in compression and makes good bulkheads. While the foam is closed cell, it will absorb or trap water. I say trap because if you stand it up, it will drip out over time. How much water the foam traps depends on the foam. The really light stuff (2-3 lb per cubic foot) like what is used in surf boards, traps water badly and is hard to get out. the heavier stuff (6+ lb per cubic foot) will trap only a little and will dry if it does get wet. Styrofoam is used because it is really cheap and easy to buy. There are other foams, PVC and polyurethane are fairly common. Rigid polyurethane is used for building insulation and I buy PVC at a upholstery supply company (I have no idea what they use it for)

If you are worried about water. Make the skin a little thicker and dissolve out the foam with gasoline when you are finished. For carbon /foam boards more than 90% strength is in the skin. There are a lot of little tricks to foam core. Coating the core to strengthen it before you start really working on it or is when the foam gets too thin, you stop it. It is solid past that point.


In terms of joining hollow core wood. The are many ways. I know of one that works but it may not be the best. In general you build up the edges with additional layers of wood . When sand the joining surfaces flat you have 6-10mm wide surfaces to glue together. It is also a good idea to add a central spar. The spar has to be fitted so it just touches both sides. The details are actually more important than the general theory where the wood gets thin like the trailing edge. Everybody has their secret method. I saw an old rudder once where the trailing edge was made separately and the skin cut to fit in the trailing edge. It looked a lot like the Marstrom except the trailing edge was some dense wood.

Oh guys,

I really appreciate all your time and input. I have downloaded
your answers to my disk in case I need these infos, but
you are way ahead of me.

All I wanted is go cat sailing And now I'm deep in
foaming. glassing, vacuum bagging, my garage looks like
hell, the house stinks of resin, my wife complains about itching and I have not been on the water yet.

Anyway, your support is great. Thank you again

Michael

hello,
Like it says in the first article that was linked to, there are 2 types of styro. the blue one he recomends is extruded and doesn't soak water. the thing he apparently doesn't know is that the bond between the glass or carbon and the extruded foam is shortlived unless specific steps are taken. the reason i know this is the winsurfboard business on Maui has been there. Thousands of boards were built with the stuff and they mostly all delamed eventually. Apparently if you vacumebag sheet foam to the extruded styro the lam will hold however. there may be other solutions which are prolly secret. The winsurfboard builders ended up staying wth the beadtype styro even though it soaks water. We encase it with sheet foam which is vacumebagged, so they only leak after a pretty good hit. these boards are custom and some are just sailable plugs for the molded versions that are made in Tailand.
you can just glass the beadtype styro by hand and as long as you get it out of the water as soon as you get a hole it will last quite a while as long as the skin is plenty strong. glassing w/ carbon lasts the longest and comes out the strongest for the weight.
styro comes in many densities. we use mostly 1.5 lb. 2 lb will be more unbreakable but heavier because if you cut back on the skin weight the board will break since styro isn't very strong. the beauty of the beaded 1.5 lb styro is that it is very easy to shape. Both with a hot wire and with the planner/sandpaper process. Shaping extuded styro is almost as tough as shaping wood.
As far as hollow molded daggerboards go, i would imagine that they are done in an autoclave w/ prepreg and the process would be a carefully guarded secret, or at least you would have to go to school to learn about that process.

Probably would make some of you ROFL, but here is my first
shot at my daggerboards, (picture attached), 1/4 inch plywood initially, sanded down at the aft edge, with 2 layers of mats now. I assume they dont have much in commeon with the real ones from SOL CAT, but I had only some pictures of Cats and just tried to figure out how they might look

If they work, I'll try to stabilize them and get the front part thicker to get some better shape.

Thanks for all your insight again

Michael

Look like daggerboards to me. One more thing. Put a big thick piece of rope through the top so they cannot possibly slip into the trunk. If they do, they immediatey bust out the inside of the trunk (simmultaneously) and then you sink and spend the rest of the week end retrieving your boat (what is left) and then everyone laughs at you and ... put a big thick piece of rope.

Also-
I can't remember how the Sol Cats keep the boards down, but what I remember from sailing a Sol Cat is the stock boards are HEAVY- ie they sink. Your new boards will likely float, ie when you put them down they will tend to float up. Use a system like the Nacras- originally they used a bunji from the top front of the board going forward to the hull then switched to a "side loader"- a rubber covered bit of PVC as long the board with a bunji loop running through it and connected to hooks/loops so the tube has to be pulled slightly to the side to put the board in so the loop puts a sideways pressure on the board which will keep it up and down.
Just a thought-

Kirt

David, thanks for the warning, will certainly heed that.
At the moment, they will probably be able to fall just through, because they are the same thickness top or bottom.

Kirt, I think I saw a picture describing what you said.

I big bungee going from the hole to the front beam,
so the board is some kind of jammed in the slot.
I think I'll try that (with the rope )

Thanks for the support.

Michael